In many situations, apparatuses must operate in potentially hazardous conditions, such as where a fuel mixture may be ignited by uncontrolled operating or environmental conditions. For example, vehicles, including aerospace vehicles, typically operate with a fuel that must be maintained in a safe condition during storage and use. The ignition hazard should be minimized even when the vehicle is subject to uncontrolled events such as an accident, electrical malfunction, a lightning strike, or static electrical discharge. Other applications requiring ignition hazard consideration include fuel transport, fuel storage, mining operations, chemical processing, metal fabrication, power plant construction and operation, and operations which involve combustible particulate such as sawdust, metal, flour, and grain.
Design of apparatuses exposed to ignition hazards typically involves reducing the likelihood of ignition, containing the ignition hazard, and/or withstanding the ignition hazard. Test systems may facilitate or verify the design of a component by simulating or applying ignition hazard precursors such as heating, a simulated lightning strike, or other electromagnetic effects (e.g., arcing, electrostatic discharge, and/or hot particle ejection).
In the aerospace industry, the Federal Aviation Administration (FAA) requires ignition source tests for components potentially exposed to fuel-vapor environments (specified in SAE ARP 5416A (SAE Aerospace)). One test method is the ignitable mixture (flammable gas) test method. In the ignitable mixture (flammable gas) test method, a test article that represents the component is subjected to an ignition hazard precursor (e.g., simulated lightning strike) in a flammable atmosphere within a test chamber. If the test article produces an ignition hazard (electrical arc) above a predefined energy limit of 0.2 mJ (millijoules), the flammable atmosphere explosively ignites in the test chamber. The test chamber is designed to enclose the test article such that the flammable atmosphere does not leak and become a hazard, and such that the explosive ignition is contained and rendered non-hazardous.
The drawbacks to this approach include expensive test chambers, limited test article and test chamber sizes (due to both safety and cost), long test setup times (due to filling large volumes with flammable gases), and long preparation times (due to test chamber fabrication).
Further, design of large and complex apparatuses would be facilitated by testing larger and/or more representative test articles (e.g., components or the entirety of a wing fuel tank of an aircraft). However, testing larger articles with conventional techniques involves consequently larger test chambers and/or larger amounts of combustible material (such as fuel in the test article and/or flammable gases to detect ignition sources).